Physics - 2.1 - Velocity

VelocityIB PHYSICS | UNIT 2 | MOTION

What is Motion?

Relative to the earth: Moving 17,500 mph

Relative to the shuttle:Not moving

An object's change in _____________ relative to a reference point.

position

Distance vs. Displacement

Distance

Displacement

How far travelled

How far from origin

Try this | Distance and Displacement

You walked 3 miles East, turned left, then walked 4 miles North. What is your distance? displacement?

Distance 7 miles

Displacement 5 miles

5

3

4

Constant Displacement

Not moving

Dis

tan

ce (

m)

Time (s)

Vel

oci

ty (

m s

-1)

Time (s)

Average Speed and Velocity

Average Speed =𝑇𝑜𝑡𝑎𝑙 𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒

𝑇𝑜𝑡𝑎𝑙 𝑇𝑖𝑚𝑒

Average Velocity =𝑇𝑜𝑡𝑎𝑙 𝐷𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑚𝑒𝑛𝑡

𝑇𝑜𝑡𝑎𝑙 𝑇𝑖𝑚𝑒

* Always Positive

* Includes Direction

Calculating Average Speed

New world record for a marathon (26.2 miles) was set several years ago. David Kimetto finished in 2.04 hours. What was his average speed?

𝑣 =𝑑

𝑡=26.2

2.04= 12.8 mi hr−1

Marathon Runners are FAST

Consider this…

The gold medalist for the men’s 400 m (one complete lap of the track) in Rio was Wayde van Niekerk with a WR time of 43.03 s. What was his average speed? Average velocity?

𝐴𝑣𝑔 𝑆𝑝𝑒𝑑 =400 𝑚

43.03 𝑠= 9.3 𝑚 𝑠−1𝑠

𝐴𝑣𝑔 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 =400 𝑚

0 𝑠= 𝟎𝒎 𝒔−𝟏

What is a Vector?

A Vector is a quantity that includes both direction and magnitude

Vector vs Scalar

Vector Quantities Scalar Quantities

Displacement Distance

Velocity Speed

Force Energy

Racing against Usain…

In 2012, Usain Bolt’s Gold Medal 100 meter dash took just 9.63 seconds.

In 1896, the gold medalist finished in 12.00 seconds.

Making the assumption that they are traveling at a constant velocity (they aren’t really), how far behind Usain would the 1896 medalist be?

100 −9.63

12100 = 𝟏𝟗. 𝟕𝟓 𝐦

100

12= 8.3 m s−1 8.3 m s−1 9.63 s = 80.25 m

100 − 80.25 = 𝟏𝟗. 𝟕𝟓 𝐦

Method 2:

Method 1:

Plot this problem on a D vs T graphD

isp

lace

men

t (m

)

Time (s)

20

40

60

80

100

2 4 6 8 101 3 5 7 9 11 12

120

80.25 m

Racing against Usain…

Constant Positive Velocity

Changing position at a constant rate forward

Dis

pla

cem

ent

(m)

Time (s)

Vel

oci

ty (

m s

-1)

Time (s)

Constant Negative VelocityD

isp

lace

men

t(m

)

Time (s)

Vel

oci

ty (

m s

-1)

Time (s)

Changing position at a constant rate backward

Plotting Displacement vs TimeD

isp

lace

men

t (m

)

Time (s)

Which runner was moving the fastest?

RunnerA

RunnerB

RunnerC

Steeper Slope

The power of the slope!

Slo

pe Displacement vs Time

Velocity vs Time

What is the Average Velocity?D

isp

lace

men

t (

m)

Time (s)

20

40

60

80

100

2 4 6 8 101 3 5 7 9 11 12

120 𝑠𝑙𝑜𝑝𝑒 =𝑟𝑖𝑠𝑒

𝑟𝑢𝑛=∆𝑥

∆𝑦

m

s= m s−1

100

8= 12.5

12.5 m s−1